It is often desirable to backsurge fluid through the well casing perforations and perforation tunnels which interconnect a well with the surrounding reservoir. This tends to flush out any perforation gun debris or other solid particles that might impede the flow of fluid.
As indicated by the McCauley, Barnes and Suman U.S. Pat. No. 3,743,021, in many wells, such a backsurging can be mechanically induced by a rapid intake of fluid into low pressure chambers positioned within the casing. But, in relatively shallow wells, or wells in pressure-depleted reservoirs, a mechanically-induced backsurging may be difficult or undesirable. The lack of pressure differential into the wellbore may make it hard to arrange a low pressure chamber capable of providing enough pressure drop to effectively backflush the perforations.
A copending patent application by E. A. Richardson and R. F. Scheuerman, Ser. No. 902,636, filed May 4, 1978, describes a process for initiating a generation of a controlled amount of nitrogen gas within a wellbore and/or an adjacent reservoir. The gas-generating process is used to initiate a production of fluid from a well from which the production is impeded by the hydrostatic pressure of the liquid in the wellbore. In the process of the 902,636 application, the gas-generating liquid contains both a compound that can be oxidized to yield nitrogen gas and an oxidizing agent capable of effecting the oxidation. The composition of the gas-generating liquid is correlated with the pressure, temperature and volume properties of the reservoir and well conduits so that the pressure and volume of the generated gas causes liquid to be displaced from the wellbore. Enough liquid is displaced to reduce the hydrostatic pressure to less than the fluid pressure in the adjacent portion of the reservoir and cause fluid to flow from the reservoir. The disclosures of the 902,636 application are incorporated herein by cross-reference.
We have now discovered that (a) the gas-generating reaction process of the 902,636 application can operate in the presence of both a reaction-delaying buffer and a buffer-overriding reactant, (b) the so-modified solution can be injected through a wellbore and into a reservoir to there provide a very fast-rising pulse of both fluid pressure and heat within a near-well portion of the reservoir, and (c) such a provision of such a pulse can initiate a perforation-cleaning backsurge of fluid through the perforations in a well casing.